1. Field of the Invention
The present invention relates to a linear guide bearing for use in an industrial robot and, in particular, to such linear guide bearing which can reduce the operating sound thereof.
2. Description of the Related Art
Recently, in a factory for manufacturing a mechanical apparatus, there have been introduced various kinds of industrial robots so that a welding operation and a painting operation can be carried out by the industrial robots instead of an operator. An industrial robot is composed of a base to be fixed to the floor surface of a factory, motion elements such as arms and wrists which are connected to each other, and various actuators for driving these motion elements. In case an actuator is initiated in response to an instruction from a control unit, the arms and wrists of the industrial robot perform linear motions or rotary motions, so that a welding gun or a spray gun mounted on the leading end of each wrist is allowed to approach and part away from a work to thereby perform a welding operation or a painting operation on the work. In the industrial robot, to allow the motion elements to perform the linear motion, it is necessary to provide not only an actuator which allows a component member (a linear motion body) on the moving side to advance or retreat with respect to a component member on the fixed side but also a rail or a linear guide bearing which is used to allow the linear motion body to slide smoothly with no play.
The linear guide bearing is mainly composed of a rail including two axially extending ball rolling grooves respectively formed on the two side surfaces thereof, a bearing main body including two load ball grooves which are respectively formed opposed to the ball rolling grooves to thereby form two load side ball passages between the ball rolling grooves and themselves, and a large number of balls respectively interposed in the load side ball passage. In the linear guide bearing, since the balls are allowed to roll along the load side ball passages, the play and resistance of the bearing main body in the moving operation thereof can be controlled down to a very low level. Because the balls move at a speed substantially half of the speed of the bearing main body, a return side ball passage must be formed in the bearing main body and, at the same time, two end caps, each of which includes an arc-shaped ball reversing passage for communicating the load side ball passage and return side ball passage with each other, must be mounted respectively on the moving-direction end portions of the bearing main body to thereby form a ball endless circulating passage. Also, referring further to the structure of each of the ball reversing passages, from the viewpoint of machining it, the outer peripheral side portion thereof is formed in its associated end cap, while the inner peripheral side portion thereof is formed in a return guide which is interposed between the bearing main body and end cap. By the way, conventionally, there is also developed a linear guide bearing in which separators (normally, disks each having an end face formed as a concave-shaped spherical surface) formed of synthetic resin are respectively interposed between the two mutually adjoining balls to thereby control noises and surface wear which are caused by the mutual collision of the balls.
However, in the above-mentioned linear guide bearing, in operation, substantial noises are produced and thus an improvement over the noise production is desired.
That is, as shown in FIG. 22, the ball 11 rolls within the load side ball passage 21 in a state where it is in pressure contact with the ball rolling groove 3 and load ball groove 23. And, in order to obtain the smooth rolling of the ball 11, the ball 11 moves with a given clearance with respect to the peripheral wall of the passage within the return side ball passage (not shown) formed in the bearing main body 7 or within the ball reversing passage 27 which is formed in the end cap 9 and return guide 33.
For this reason, when the ball 11 advances from the load side ball passage 21 into the ball reversing passage 27, or when the ball returns from the ball reversing passage 27 to the load side ball passage 21, the ball 11, which is temporarily removed from holding or restraint, collides with the peripheral wall of the ball reversing passage 27 or with the ball rolling groove 3 and load ball groove 23. Especially, the collision sound of the ball 11 with the ball rolling groove 3 and load ball groove 23 provides the major factor in the noise production. In FIG. 22, reference numeral 31 designates a tongue portion which is formed in the end cap 9. The ball 11 returning from the ball reversing passage 27 to the load side ball passage 21 is not held or restricted until it advances into the load side ball passage 21 after it parts away from the tongue portion 31. Also, reference character a designates an angle formed between a straight line connecting the center of curvature O of the ball reversing passage 27 to the leading end of the tongue portion 31 and the moving-direction end face of the bearing main body 7. Reference character R designates the radius of curvature of the ball reversing passage 27.
In order to solve this problem, in JP-59-103928U, there is proposed a linear guide bearing in which, in the boundary portion between the load side ball passage and ball reversing passage, the leading end of the tongue portion (the ball rolling groove side end portion) of the end cap is positioned in the tangent position of the ball outside diameter in the load side ball passage. With use of the linear guide bearing thus structured, when the ball moves between the load side ball passage and ball reversing passage, the ball rolls smoothly with no bump and, therefore, the linear guide bearing can be operated smoothly with good operation performance. However, in this linear guide bearing, since the ball rolling groove in the rail must be set very shallow, it is inevitable that the load capacity of the guide bearing is lowered greatly. Also, in order to eliminate a level difference between the load side ball passage and ball reversing passage, high dimensional accuracy must be secured in the ball rolling groove of the rail as well as in the tongue portion of the end cap. However, this increases the machining costs of them and lowers the yield rate of the product.
On the other hand, in the linear guide bearing, since the ball is made to move with a given clearance with respect to the peripheral wall of the ball reversing passage, the passage diameter of the ball reversing passage must be set larger than the diameter of the ball. However, this raises a fear that the moving track of the ball within the ball reversing passage can meander. Therefore, in the conventional linear guide bearing, there is produced resistance against the ball passing through the connecting portion between the ball reversing passage and load side ball passage, so that the smooth circulation of the ball can be interfered by such resistance.
In order to solve this problem, in JP-A-7-208467, there is proposed a linear guide bearing in which each ball reversing passage is composed of a pipe body to be contacted with a ball at three points to thereby restrict the meandering motion of the ball. However, in this linear guide bearing, in the portion thereof where the ball moves from the ball reversing passage to a load side ball passage, after the ball is set free from the holding of the ball reversing passage, the ball is temporarily free from any restraint until it is restricted by the load side ball passage; and, therefore, due to the above-mentioned meandering motion of the ball, the performance of the operation as well as the noise characteristic of the linear guide bearing are degraded. Also, since little clearance exists between the pipe body and ball, not only to machine the linear guide bearing is difficult but also the manufacturing cost of the linear guide bearing is increased. On the other hand, the present inventors et al. have also tried to reduce, in the load side ball passage side portion of the ball reversing passage, the clearance between the ball and the peripheral surface of such portion down to a very small one. However, it has been found that, in this case, in such portion, the smooth rotation of the steel ball along the ball passage is interfered to thereby increase the passing resistance of the steel ball.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional linear guide bearings. Accordingly, it is an object of the invention to provide a linear guide bearing which can reduce the operation noise thereof without degrading the performance of the operation thereof.
In attaining the above object, according to a first aspect of the invention, there is provided a linear guide bearing for guiding a linear motion body along a rail including two ball rolling grooves respectively so formed on the two side surfaces thereof as to extend in the axial direction thereof, the linear guide bearing comprising: a bearing main body including two load ball grooves respectively formed opposed to the ball rolling grooves to thereby form two load side ball passages respectively between the two ball rolling grooves and themselves, and two return side ball passages respectively so formed as to extend substantially in parallel to the load ball grooves; two end caps respectively fixed to the moving-direction two end faces of the bearing body, each of the end caps including a concave-arc-shaped groove for defining the outer peripheral side portion of an arc-shaped ball reversing passage which connects together the load side ball passage and return side ball passage, and a tongue portion for forming the ball rolling groove side end portion of the concave-arc-shaped groove; two return guides respectively interposed between the bearing main body and two end caps for defining the inner peripheral side portions of the two ball reversing passages; and, a large number of balls so disposed as to circulate through the load side ball passages, return side ball passages and ball reversing passages, wherein, when an angle formed between a straight line connecting the leading end of the tongue portion to the center of curvature of the ball reversing passage and the moving-direction end face of the bearing main body is expressed as xcex1, this angle xcex1 is set in the range of 5xc2x0-20xc2x0.
According to the first aspect of the invention, when the ball passes through between the ball reversing passage and load side ball passage, the distance where the ball is not restricted can be reduced down to a very small distance, thereby being able to minimize the noise caused by the collision of the ball against the peripheral wall of the ball reversing passage or against the ball rolling groove or load side ball groove.
Also, according to a second aspect of the invention, there is provided a linear guide bearing for guiding a linear motion body along a rail including two ball rolling grooves respectively so formed on the two side surfaces thereof as to extend in the axial direction thereof, the linear guide bearing comprising: a bearing main body including two load ball grooves respectively formed opposed to the ball rolling grooves to thereby form two load side ball passages respectively between the two ball rolling grooves and themselves, and two return side ball passages respectively so formed as to extend substantially in parallel to the load ball grooves; two end caps respectively fixed to the moving-direction two end faces of the bearing body, each of the end caps including a concave-arc-shaped groove for defining the outer peripheral side portion of an arc-shaped ball reversing passage which connects together the load side ball passage and return side ball passage, and a tongue portion for forming the ball rolling groove side end portion of the concave-arc-shaped groove; two return guides respectively interposed between the bearing main body and two end caps for defining the inner peripheral side portions of the two ball reversing passages; and, a large number of balls so disposed as to circulate through the load side ball passages, return side ball passages and ball reversing passages, wherein, in the load side ball passage side end portion of at least one of the return guide and bearing main body, there is formed a chamfer having an angle xcex2 with respect to the load side ball passage, and also wherein, when an angle formed between a straight line connecting the leading end of the tongue portion to the center of curvature of the ball reversing passage and the moving-direction end face of the bearing main body is expressed as xcex1, a difference between xcex2 and xcex1 is set to be 20xc2x0 or less.
According to the second aspect of the invention, in the connecting portion between the ball reversing passage and load side ball groove, the vector of the ball in the rotation direction thereof is substantially equal to the inclination of the chamfers, so that the ball can be moved smoothly to thereby enhance the performance of the operation of the ball as well as reduce the noise thereof.